The system has three visible components designated Iota Orionis A, B and C. Iota Orionis A has also been resolved using speckle interferometry and is also a massivespectroscopic binary, with components Iota Orionis Aa1 (officially namedHatysa/hɑːˈtiːsə/), Aa2, and Ab.
ι Orionis (Latinised toIota Orionis) is the system'sBayer designation. The designations of the three constituents asIota Orionis A,B andC, and those ofA's components -Iota Orionis Aa1,Aa2, andAb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by theInternational Astronomical Union (IAU).[13]
The system has the traditional nameNair al Saif, from the Arabicنيرالسيفnayyir as-sayf "the Bright One of the Sword", though this is little used.[14][15][16]SinceAntonín Bečvář's 1951Atlas Coeli, it has borne the proper nameHatysa. Kunitzsch was unable to find an older source for the latter name.[17]
In 2016, the IAU organized aWorking Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[19] It approved the nameHatysa for the component Iota Orionis Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[20]
ι Orionis is the bright star to the right (south) of theOrion Nebula
Iota Orionis has a parallax of1.40±0.22 mas in theHipparcos new reduction,[1] indicating a distance around700 pc. The previous publishedHipparcos parallax was2.46±0.77 mas, suggesting a closer distance.[21]Gaia Data Release 3 has individual parallaxes for the two fainter components of the Iota Orionisstar system of2.7870±0.0476 mas and2.6058±0.0242 mas,[8][22] indicating distances of359 pc and384 pc respectively, with margins of error of just a few parsecs. There is little doubt that all three stars are at the same distance.[3][9]
Iota Orionis is generally assumed to be associated with the open cluster NGC 1980, which is at a distance of around400 pc. However, they may not lie at exactly the same distance and Iota Orionis may have a complex history involving stellar encounters and runaway stars.[23]NGC 1980 contains few bright stars other than Iota Orionis. Only eighteen other stars are considered members in a survey down to 14th magnitude, most of them around 9th magnitude but including the 5th magnitude starsHR 1886 and1887.[24]
Iota Orionis is dominated by the multiple star Iota Orionis A. It is clearly identified as a double-lined spectroscopic binary whose components are astellar class O9 III star (blue giant) and a class B0.8 III/IV star about 2 magnitudes fainter.[3] The combined spectral type has long been accepted as O9 III and it was listed as a standard star for that type.[25] The collision of thestellar winds from this pair makes the system a strongX-ray source. Oddly, the two objects of this system appear to have different ages, with the secondary being about double the age of the primary. In combination with the higheccentricity (e=0.764) of their 29-day orbit, this suggests that the binary system was created through a capture, rather than by being formed together and undergoing a mass transfer. This capture may have occurred, for example, through an encounter between two binary systems, with one star being donated from each binary and tworunaway stars being ejected.[3][26] A third component155 mas away has been identified usingspeckle interferometry and is probably a B2 subgiant.[4][12]
The primary component of Iota Orionis A is a class Ogiant star with a mass of about 23 M☉. It has a surfacetemperature of32,500 K and radius of 8.3 R☉, resulting in abolometric luminosity of 68,000 L☉. It is calculated to be around nine million years old. The secondary star of thespectroscopic binary pair is a class B giant orsubgiant with a mass of about 13 M☉. It has a temperature of27,000 K and radius of 5.4 R☉, resulting in it radiating over 8,000 times as much energy as the sun.
^abcNicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System".Astronomy and Astrophysics Supplement Series.34:1–49.Bibcode:1978A&AS...34....1N.
^abKazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2011). "The 80th Name-List of Variable Stars. Part I - RA 0h to 6h".Information Bulletin on Variable Stars.5969: 1.Bibcode:2011IBVS.5969....1K.
^abEvans, D. S. (June 20–24, 1966). Batten, Alan Henry; Heard, John Frederick (eds.). "The Revision of the General Catalogue of Radial Velocities".Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30.30. University of Toronto:International Astronomical Union: 57.Bibcode:1967IAUS...30...57E.
^abcdeConti, P. S.; Loonen, J. P. (1970). "Coarse analysis of the helium weak B star Iota Ori B".Astronomy and Astrophysics.8: 197.Bibcode:1970A&A.....8..197C.
^Uesugi, Akira; Fukuda, Ichiro (1970). "Catalogue of rotational velocities of the stars".Contributions from the Institute of Astrophysics and Kwasan Observatory.University of Kyoto.Bibcode:1970crvs.book.....U.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets".arXiv:1012.0707 [astro-ph.SR].
^Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.; Scholz, R.-D. (2004). "Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas".Astronomische Nachrichten.325 (9): 740.Bibcode:2004AN....325..740K.doi:10.1002/asna.200410256.
^Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978).Revised MK Spectral Atlas for stars earlier than the sun.Bibcode:1978rmsa.book.....M.
^Parenago, P. P. (1954). "Untersuchung der Sterne im Gebiet des Orion-Nebels. Tabelle III: Katalog der genauen Positionen. (Bestimmung von photographischen Beobachtungen)".Publ. Astr. Inst. Sternberg.25: 393.Bibcode:1954TrSht..25....1P.
